In drum pulpers, recycled fiber material is defibered to fiber pulp. The process is carried out so that a pulper drum rotates substantially horizontally or in a position slightly inclined from the material feed end to the exit end and material to be defibered rises up in the rotating drum and at some point, falls down to the bottom and is defibered. The size and rotation speed of the pulper drum are designed according to the pulper capacity so that material fed to one end of the drum would be defibered as well as possible when it reaches the exit end. Current drum pulpers do not have actual controls, and the only typical variables are chemicals used and the amount thereof as well as consistency of pulp to be pulped, which is a constant value regarded as suitable for the pulper and the pulp type.
The aim of drum pulping is to separate fibers from each other as well as possible, thereby keeping the size of different impurities, such as plastic, glues etc., as large as possible to facilitate their separation from fiber pulp. By using current drum pulper solutions, however, it is not possible to optimize the process in practice.